The goal of this project is to increase our knowledge of the nature and behavior of dental amalgam which will serve as a basis for improving the clinical performance of this restorative material. To achieve this goal, several areas of activity will be undertaken; (1) characterizing clinical behavior, (2) identifying in vitro property tests for predictability of clinical behavior, (3) relating composition and phase structure to clinical behavior, and (4) developing a new amalgam system. In the area of clinical behavior, the efficacy of bonding amalgam to tooth structure will be assessed by comparing marginal fracture of restorations that have been placed with and without a bonding adhesive. If bonding is effective crevice corrosion will be eliminated and marginal degradation will be reduced. The microstructural nature of gamma2-free amalgams in clinical service for at least 10 years but requiring replacement will be retrieved and characterized. The availability of these restorations is a result of a clinical study in our facility for the past 24 years in which 20 gamma-2-free amalgams have been investigated. This will serve as a model in the development of an in vitro conditioning environment for laboratory test specimens. The results of physical property tests on specimens stored in this conditioning environment will then be compared to our clinical performance data to assess test predictability. Of particular emphasis will be to identify tests that relate to the reported differences in clinical performance of the gamma2-free amalgams. Composition and phase structure of in vitro specimens will be determined by microprobe analysis to identify relationships to the clinical performance of these same alloys. An amalgam system utilizing and Ag3Sn/Cu3Sn admixture alloy will be investigated to provide a new approach to dental amalgam systems. In this system, other elements which may provide significant improvements can be efficiently introduced and tested for merit.